The present invention relates to an apparatus for the detection and recording of uterine activity.
Monitoring and evaluation of uterine activity, which permits the determination of the presence of contractions, is important in perinatal medicine for monitoring the course of pregnancy and evaluating the state of the fetus.
Essentially two methods, an internal and an external method, are known for detecting and recording the intrauterine pressure in the form of a tocogram. Both methods have in common that the uterine pressure is measured at the body by means of pressure sensors.
For internal tocography, the pressure is determined by introducing a fluid-filled, open end catheter into the amnionic cavity or between the amniotic sac and the wall of the uterus. After zero matching has been effected, it is possible with this method to determine the absolute pressure of the uterus.
The internal tocography method is rejected by many physicians due to the difficulty of operation and the risk factor involved. Moreover, most recent tests show that the application of a catheter influences parturition so that this process should not be used for impending permature deliveries where monitoring of the contraction activity would be of particular significance.
External tocography is based on a method disclosed by Rech in 1934. A pressure sensor, which is normally an expansion measuring strip, is fastened to the abdomen of the pregnant patient by means of an elastic strap. Uterine contractions produce changes in the displacement of a sensor pin which acts mechanically on the expansion measuring strip, so that an electrical signal is derived which is a measure for the contraction activity and whose waveform can be evaluated by the treating physician.
External tocography has the drawback that it is an indirect method of pressure recording and is therefore subject to many interfering influences which falsify the measuring result. Such interfering influences include, for example, the changes in pin displacement simply as a result of breathing. This non-invasive method is based on the assumption that the pressure sensed and recorded by the sensor pin constitutes a sufficient approximation of the intrauterine pressure. However, no exact information about the course of the uterine activity can be obtained with this measurement.
Thus both methods have significant drawbacks during routine clinical use so that evaluation of uterus mobility is not used very often and does not produce the results that should be expected from the capability of this method.